Current and future aircraft are expected to operate more economically than their predecessors under more stringent environmental and airspace constraints. Aircraft engine-integrated drag management technologies have been identified as one way to achieve future operational improvements, such as lower-noise approaches that benefit from reduced engine thrust on approach and descent.
Conventional systems for managing aircraft drag are unsatisfactory in a number of respects. For example, airframe drag generating components are often noisy and place the aircraft in an aerodynamic configuration that requires relatively high engine idle inertia to enable emergency procedures where rapid acceleration is required.
Generation of swirling outflow from the engine's exhaust has the potential to deliver equivalent drag at a given engine operating condition without the need for such noisy airframe-based components. However, technologies to generate such swirl require structures configured to partially redirect the stream of fluid exiting the nozzle of the turbofan engine in a manner that can rapidly and reliably return the engine to a high thrust mode when necessary.
Commonly known components used in such systems—e.g., turning vanes and other such structures—are not stowable in a manner that is optimal. That is, even when not deployed, the geometry and placement of such swirl vanes and other structures can change the flow path of fluids within the turbofan engine, resulting in a drag penalty for the aircraft when in a cruise configuration. Additionally, conventional turning vanes may reduce nozzle flow capacity, resulting in a potentially adverse back pressuring of the engine's pumping system.